1. Field
The field of the invention is endless track assemblies for snow grooming vehicles, and more particularly the belt and cleat assemblies thereof, including structures for fastening the cleats to the flexible belting used in such tracks.
2. State of the Art
Snow groomer vehicles use endless tracks made up of fabric reinforced flexible plastic belts made continuous by lacing their ends together. Actual lacing thread may be used, although lacing joint assemblies are more commonly employed, being combinations of metallic hinge plates and associated hinge pins. The snow grooming vehicle commonly has an endless track assembly on each of its sides, each comprising a number of the fabric reinforced plastic belts. The belts are spaced apart to provide a broad base for the track while utilizing minimum amounts of belting. Steel cleat assemblies are bolted across the individual belts at intervals, tieing them together into a track assembly. Holes for cleat mounting bolts are provided through the belts. Each assembled track is engaged by a power-transmitting sprocket wheel, which forces the belts to travel together around a set of guiding wheels called bogies. The powered belt imparts horizontal shear forces to the cleats, which engage the snow to propel the vehicle. Extensive development has gone into the design of the elongate cleat members, with the objectives of providing maximum forward traction along with substantial resistance to side slipping. Cleat constructions are disclosed in U.S. Pat. Nos. 3,765,731, 4,560,211, 4,281,882, 4,059,315 5,199,771 and 5,201,574. Typically, the ground contacting cleat, also called a "grouser", is fastened to the outside of the flexible belting by bolt and nut assemblies installed in matching holes through the grouser, the belt, and a metal backing plate on the inside of the belt. A large number of bolt and nut assemblies are required to spread the high shearing forces among the belt holes. The horizontal force on the ground engaging part of the cleat also results in high moment loads which must be resisted by the stems of the bolts. Failure of the bolts in bending is a too frequent common occurrence. U.S. Pat. No. 5,201,574 and application Ser. No. 08/096,187 disclose assemblies designed to substantially decrease cleat mounting bolt failures. The present application however is directed to improvements in the structure of the belt itself, as well as to cleat attachment provisions.
Prior art endless belts utilize a fabric reinforced plastic. The belt must be substantially non-elastic in tension but flexible enough to bend to pass around the sprocket and bogies. The need for tensile strength has resulted in quite thick, stiff track belts incorporating high percentages of the stretch resisting fabric. Because of the stiffness of the belt, a very significant amount of power must be expended to continually force it to bend about the sprocket and bogies during operation. A more flexible, stretch resisting belt with the requisite high tensile strength is needed.
The prior art methods of attachment of the cleat assemblies also requires that the belts be stiff and thick. Considerable belt thickness is needed to resist high forces which bear against the sides of the mounting bolt holes. The cleat loosening from bolt hole deformation and enlargement is an ever present problem. This loosening inevitably occurs from creep of the plastic material under both operational and clamping forces over extended periods.
This loosening is serious in itself, but it also leads to ingress of water into the very center of the belt structure. Soaking action reduces belt structure integrity and leads to reduced belt life. The belts must operate in cold weather, so that the penetrating water freezes with still further destructive results.
The need then is not only for a more flexible belt, but also for a method of cleat attachment which will not allow ingress of water into the interior of the plastic of the belt.